The present invention relates to a fixing sleeve for optical cables.
A particularly advantageous application of the invention lies in the field of laying optical cables inside buildings.
In order to lay optical cables inside a building, it is known that said cables can be inserted in precabling tubes that are initially installed in the infrastructure of buildings and that are designed for this purpose, for example cable ducts.
Optical cables are installed in precabling tubes in conventional manner using various techniques such as carrying, blowing, pulling or pushing, for example. In general, the optical cables are mounted so as to be free inside the tubes, which means that they are particularly exposed to various stresses, such as traction or bending stresses at the points where they leave the tubes. These stresses are usually generated by the handling that is applied to cables during a connection operation, for example, and they run the risk of damaging the cables severely if they fail to comply with limit values, particularly concerning the radius of curvature of the cables.
One object of the present invention is to hold an optical cable still in order to avoid harmful traction movements.
Another object of the present invention is to limit cable bending to some minimum radius of curvature.
These and other objects are attained in accordance with one aspect of the present invention directed to a fixing sleeve that comprises, along a common axis, both a first portion that is substantially cylindrical and a second portion that is substantially conical, said first and second portions being pierced by an axial bore, and in that the sleeve carries along its entire length a continuous slot communicating with said axial bore, the slot comprising a longitudinal first slot in the first portion of the sleeve, and a spiral second slot in the second portion of the sleeve.
Thus, as explained in greater detail below, when an optical cable is placed in the fixing sleeve of the invention, which sleeve is inserted in a precabling tube via said first portion, the optical cable is held in place inside the axial bore which extends along the entire length of the sleeve, thereby significantly limiting movements of the cable inside the sleeve. In particular, longitudinal movement can be greatly reduced because, in accordance with the invention, said axial bore has an irregular wall that is corrugated or granular, for example, thereby increasing friction between the cable and the bore. Nevertheless, it should be observed that the spiral shape of the second slot does indeed allow the cable to bend to a certain extent so as to enable it to accommodate particular geometrical configurations where the cable needs to be curved by a given amount in any direction. Nevertheless, this bending remains controlled and limited to a maximum amount of curvature which is determined by the conical shape of the second portion, the pitch of the spiral, and the elasticity of the material constituting the fixing sleeve of the invention.
In order to make it easier to insert the fixing sleeve in precabling tubes, provision is also made in the invention for said first portion to be slightly frustoconical. This disposition also has the advantage of holding the cable more securely in the axial bore since the radial forces developed while inserting the sleeve in the tube tend to clamp the cable more firmly inside the bore. This advantageous effect is made even more perceptible when said sleeve is made of elastomer.
It should also be observed that an optical cable can be put into place in the fixing sleeve of the invention very simply and quickly, since it suffices to open the continuous slot in the sleeve by acting against the elasticity of the sleeve material, to insert the cable therein, and then allow the slot to reclose under the effect of the sleeve returning elastically to its initial shape. There is thus no need to cut the cable or to thread it through the sleeve. Inserting the cable into the sleeve is made even easier when, in accordance with the invention, said first longitudinal slot has an insertion flare at one end.
Finally, the invention presents other advantages such as protecting cables in precabling tubes and closing said tubes so as to seal them effectively against foreign bodies (dust etc.).